cmake: really enable warnings with clang

Even though `PICKY_COMPILER=ON` is the default, warnings were not
enabled when using llvm/clang, because `CMAKE_COMPILER_IS_CLANG` was
always false (in my tests at least).

This is the single use of this variable in curl, and in a different
place we already use `CMAKE_C_COMPILER_ID MATCHES "Clang"`, which works
as expected, so change the condition to use that instead.

Also fix the warnings uncovered by the above:

- lib: add casts to silence clang warnings

- schannel: add casts to silence clang warnings in ALPN code

  Assuming the code is correct, solve the warnings with a cast.
  This particular build case isn't CI tested.

  There is a chance the warning is relevant for some platforms, perhaps
  Windows 32-bit ARM7.

Closes #9783

1 files changed, 5 insertions, 5 deletions

diff --git a/lib/setopt.c b/lib/setopt.c
index 5b5975485..6629a9f46 100644
--- a/lib/setopt.c
+++ b/lib/setopt.c
@@ -406,7 +406,7 @@ CURLcode Curl_vsetopt(struct Curl_easy *data, CURLoption option, va_list param)
     arg = va_arg(param, long);
     if((arg < CURL_TIMECOND_NONE) || (arg >= CURL_TIMECOND_LAST))
       return CURLE_BAD_FUNCTION_ARGUMENT;
-    data->set.timecondition = (curl_TimeCond)arg;
+    data->set.timecondition = (unsigned char)(curl_TimeCond)arg;
     break;
   case CURLOPT_TIMEVALUE:
     /*
@@ -1135,7 +1135,7 @@ CURLcode Curl_vsetopt(struct Curl_easy *data, CURLoption option, va_list param)
     arg = va_arg(param, long);
     if((arg < CURLPROXY_HTTP) || (arg > CURLPROXY_SOCKS5_HOSTNAME))
       return CURLE_BAD_FUNCTION_ARGUMENT;
-    data->set.proxytype = (curl_proxytype)arg;
+    data->set.proxytype = (unsigned char)(curl_proxytype)arg;
     break;
 
   case CURLOPT_PROXY_TRANSFER_MODE:
@@ -1234,7 +1234,7 @@ CURLcode Curl_vsetopt(struct Curl_easy *data, CURLoption option, va_list param)
     arg = va_arg(param, long);
     if((arg < CURLFTPMETHOD_DEFAULT) || (arg >= CURLFTPMETHOD_LAST))
       return CURLE_BAD_FUNCTION_ARGUMENT;
-    data->set.ftp_filemethod = (curl_ftpfile)arg;
+    data->set.ftp_filemethod = (unsigned char)(curl_ftpfile)arg;
     break;
   case CURLOPT_FTPPORT:
     /*
@@ -1261,7 +1261,7 @@ CURLcode Curl_vsetopt(struct Curl_easy *data, CURLoption option, va_list param)
     arg = va_arg(param, long);
     if((arg < CURLFTPSSL_CCC_NONE) || (arg >= CURLFTPSSL_CCC_LAST))
       return CURLE_BAD_FUNCTION_ARGUMENT;
-    data->set.ftp_ccc = (curl_ftpccc)arg;
+    data->set.ftp_ccc = (unsigned char)(curl_ftpccc)arg;
     break;
 
   case CURLOPT_FTP_SKIP_PASV_IP:
@@ -1289,7 +1289,7 @@ CURLcode Curl_vsetopt(struct Curl_easy *data, CURLoption option, va_list param)
     arg = va_arg(param, long);
     if((arg < CURLFTPAUTH_DEFAULT) || (arg >= CURLFTPAUTH_LAST))
       return CURLE_BAD_FUNCTION_ARGUMENT;
-    data->set.ftpsslauth = (curl_ftpauth)arg;
+    data->set.ftpsslauth = (unsigned char)(curl_ftpauth)arg;
     break;
   case CURLOPT_KRBLEVEL:
     /*